As a cruise control device for a vehicle such as an automobile, a cruise control device is already known that performs trajectory control by calculating a target rudder angle of steerable wheels for causing a vehicle to travel along a traveling road, and controlling the rudder angle of the steerable wheels so that the rudder angle coincides with the target rudder angle by using a rudder angle varying device. An exemplary cruise control device of this type is disclosed in WO2010/073400. In the cruise control device of this type, the rudder angle of steerable wheels is controlled by a rudder angle control device so that the rudder angle coincides with a target rudder angle, independently from a steering operation by a driver.